1. Field of the Invention
The present invention relates to a breather structure of an engine, and more particularly to a breather chamber separating an air including an oil mist within the crank case into oil and gas.
2. Prior Art
In general, a breather chamber of the engine is formed in an upper wall portion of the crank case away from the cylinder. Particularly, in an engine provided with a transmission chamber in a rear portion of the crank case, as described in Japanese Unexamined Patent Publication No. 8-218842, the structure is made such that the breather chamber for separating oil mist from the blow-by gas is formed in an upper wall of the transmission chamber in the rear portion of the crank case, the oil component after being separated in the breather chamber is returned to a bottom portion of the transmission chamber or an oil pan.
In an engine mounted to a vehicle such as a motor cycle or the like, in order to respond to a high power requirement in recent years, a cylinder is improved by making a bore diameter large and making a thickness of the cylinder large, or forming a reinforcing rib, thereby reinforcing the cylinder, however, in the case that the thickness is increased or the reinforcing rib is independently formed, a size of the engine is increased and a weight thereof is increased.
Further, in the structure in which the oil component separated in the breather chamber is returned to an oil reservoir via an oil return oil path, in the case that an oil level of the oil reservoir is high, the oil in the oil reservoir flows back through the oil return oil path so as to be pushed back to the breather chamber, on the basis of an oil level fluctuation of the oil reservoir at a time of a rapid acceleration or a rapid deceleration, for example, a back and forth movement of the oil, or a ruffling phenomenon generated by the air pushed down by a vertical motion of the piston pushing the oil within the oil reservoir, so that there is a risk that a breather function is affected.